At the end of March, the Romney camp had captured 607 delegates and 4.1 million votes. That means the candidate, who has cultivated a reputation as a penny-pincher, spent $18.50 per vote, and $126,000 per delegate.

The money was used to cover various expenses like hotels, food, equipment, accounting services, rental cars, air travel, event consultants and online advertisers.

For instance, in March, the campaign spent $871 on Poland Spring water, $1,966 on office supplies from Apple (AAPL, Fortune 500), more than $50 at Applebee's, $48 at Arby's, $9.57 at Panda Express, $11,000 in payments to the Waldorf Astoria hotel and $70,165 at law and lobbying firm Patton Boggs.

But at least two of Romney's contenders had a better votes-to-expenditure ratio.

Gingrich, for example, spent $21 million through the end of March, collecting 141 delegates and 2.2 million votes. That works out to just under $10 per vote and around $150,000 per delegate.

Santorum spent $18.7 million on 264 delegates and 2.9 million votes for a per-vote expenditure just north of $6.50 and a cost-per-delegate of about $71,000.

Paul, meanwhile, got the worst return on his money of the final contenders. The Texas congressman spent nearly $35 million, but received only around 1.1 million votes and 72 delegates. The math works out to $32.40 per vote and roughly $485,500 per delegate.

And that's just the official campaign spending. This cycle, the influence of super PACs should not be ignored. While technically prohibited from coordinating with campaigns, the new spending vehicles acted as a supplement, and in some cases, became campaign linchpins.

When super PAC money is factored in, overall spending on Romney's behalf jumps to $122 million, bringing his cost-per-vote to just under $30. By this measure, each delegate cost more than $200,000.

Gingrich also saw a significant jump when super PAC money is included. Adding in the $18 million spent by the Winning our Future super PAC, the former House speaker's cost-per-vote jumps to over $17.75, while spending per delegate tops $275,000.

The Santorum super PAC added around $8 million in spending. That pushed him to almost $9.50 per vote and $101,500 per delegate. Less reliant on super PAC spending, Paul's figures were little changed.

Moving ahead, Romney faces the challenge of ramping up fundraising efforts, while investing a healthy percentage of that money in the kind of ground game that will be able to get out the vote in November.

One candidate has a jump on Romney in that category: President Obama. The Obama re-election campaign has brought in $191 million, and already spent just less than half -- or $89 million -- of that total.